My approach on this painting demonstration is fundamentally simple. My focus is the green apple. The dark background serves the high value of the light side of the apple. The supporting objects serve to maintain/increase focus on the green apple while adding depth and interest.
Nutshell:
Focus: Greens (expanding to yellow) and high value (light), minority of space in the composition. Most refined/detailed portion of painting.
Background and supporting objects: Reds (expanding to purple) and low value (dark), majority of space in the painting. Less refined/detailed than focal area.
Result: A composition with dramatic focus. (Hopefully ;) )
Now the tricky part...Making it happen.